Technical Field
This application relates to techniques for fabricating electronics substrates and semiconductor wafers in general, and more particularly, for example, to methods for patterning layers on such substrates and wafers using lasers and removing post-laser debris.
Related Art
Laser ablation describes the removal of materials using high photon energies (i.e. short wavelengths, and not necessarily high intensities) and is a very effective method of patterning polymers. Typically, ultraviolet (UV) light strikes the polymer at moderate intensities such that the combination of photochemical and photothermal effects dissociates the polymer chain into smaller, volatile molecules that are removed with a debris removal system. In addition to the successful removal of polymers such as polyimide, laser ablation can be used to remove metals and inorganic materials.
Laser ablation can be a cost-effective patterning method since high-resolution features can be patterned without photosensitive mediums, developers, or etchants. For example, laser ablation has been successfully used to pattern materials with a resolution limit of less than 5 μm. The laser ablation rate is a function of wavelength, pulse width, and fluence, so the ablation rate can be precisely controlled.
Laser ablation has been successfully demonstrated with excimer lasers, which have become the staple of microlithography in the past two decades. Excimer lasers are the most powerful UV laser sources, and usually contain a rare-gas and a halogen or halogen-bearing gas. Popular excimer laser gases are KrF (248 nm), and ArF (193 nm). Unlike other lasers, the excimer laser produces speckle-free and incoherent light, which is ideal for high-resolution lithography. Because excimer lasers emit light efficiently in the UV spectrum, have a large beam size, and are readily available for microlithography, they are ideally suited for laser ablation.
The laser ablation process, however, creates debris (particles of material ejected during patterning) on the surface of the material that needs to be removed. This debris contaminates the substrate and may cause difficulties with subsequent steps. Current materials used on the substrate to remove debris may not absorb the UV radiation from the laser or withstand laser scanning of a full die, and can peel, reducing their efficacy to clear debris from the surface.
Many products have been commercialized for the purpose of removal of UV laser ablation debris. These materials were mostly used for UV laser (CO2) or solid state lasers such as diode-pumped solid-state (DPSS) lasers where the process is performed one via or one line at a time. These materials such EMC 1146 protective coating for laser scribing (commercially available from Emulsitone Chemicals, LLC), Daecoat products (commercially available from John Moore Consulting), or HogoMax products (commercially available from DISCO Corporation) did not work effectively when used with mask scanning systems utilizing the excimer laser process. These materials could only be used effectively with spot shot ablation, and do not have enough UV absorption capability. Therefore, they lift or peel off when exposed to a scan beam during an excimer laser ablation process.
Many other research institutions have proposed the use of a thin layer of photoresist material as a sacrificial layer. The cost and use of solvent, however, make this option unattractive in high volume manufacturing.
Accordingly, there is a need for improved materials and methods for the removal of post-laser debris.